The invention relates to improvements in apparatus for measuring the density of accumulations of fibrous material (such as tobacco or filter material) in rod making machines of the tobacco processing industry. More particularly, the invention relates to improvements in density measuring apparatus which can be utilized in machines for the simultaneous making of several rod-like accumulations of particulate materials of the type being processed in the cigarette making, cigar making and related industries.
It is already known to construct a density measuring apparatus for use in machines for simultaneous production of two tobacco-containing rods in such a way that radiation issuing from a source is caused to penetrate through moving rods of particulate tobacco and into an ionization chamber, thereupon directly into the ionization chamber, again through the moving rods, and so forth. Reference may be had, for example, to U.S. Pat. No. 4,424,443 the disclosure of which is incorporated by reference. By alternatingly directing radiation through the rods of particulate material and directly into the ionization chamber, the patented apparatus reduces the likelihood of inaccurate density measurements, e.g., due to drift. In other words, such apparatus is designed for automatic calibration in the course of the actual density measuring operation. The signals denoting the actual density include those signals (measurement signals) generated as a result of penetration of radiation through the rods and into the ionization chamber as well as those signals (reference signals) which are obtained in response to direct penetration of radiation into the ionization chamber, i.e., without passing through the rods of particulate material).